The present invention relates to a gas discharging display panel such as a plasma display panel and a manufacturing method and, more particularly, to an AC-driven gas discharging type display panel suitable for color display and capable of providing a high accuracy and high contrast display and which is inexpensive.
A gas discharging display panel such as a plasma display has such features that a view angle is wide, the display is easy to see because of self emission, and it can be fabricated with a reduced thickness, which is utilized as a display device for OA (office automation) equipments, as well as expected for application uses such as high quality television receivers.
The gas discharging type display panel is generally classified into a DC driven type and an AC driven type. Among them, the AC driven type panel has a memory function by the effect of a dielectric layer covering an electrode and has high luminosity. Further, with application of a protective film, a working life endurable to practical use can be obtained even also for the AC driven type in recent years, and it is put to practical use for example, in multipurpose video monitors.
FIG. 4 shows a perspective view of a portion of a plasma display panel which is presently used. The gas discharging type color display panel comprises a back substrate 2 and a front substrate 1 opposed to each other. The back substrate 2 has barrier ribs 3a for maintaining a gap with the front substrate 1 constant, and the front substrate 1 and the back substrate 2 are connected by way of the barrier ribs 3a. In FIG. 4, the front substrate 1 and the barrier ribs 3a of the back substrate 2 are separately shown for ease of viewing.
The front substrate 1 has a structure including display electrodes (transparent electrode) 5, buss electrodes 6 made of a metal conductor, an insulator layer 7 and an MgO film (protective film) 8 which are formed on a front glass plate 4a. The back substrate 2 has a structure including address electrodes 9, barrier ribs 3a and a fluorescent layer 14 which are formed on a back glass plate 4b. A discharging space 3f is formed between the front substrate 1 and the back substrate 2 by disposing and appending the front substrate 1 and the back substrate 2 in parallel with each other such that respective surfaces formed with the electrodes are opposed to each other. The display electrodes 5 and the address electrodes 9 are made orthogonal to each other by way of the discharging space 3f.
FIG. 5(a)-(c) and FIG. 6 show cross sectional views of the gas discharging type display panel of FIG. 4. FIG. 5(a) is a cross sectional view when cutting a portion of the display panel along a plane parallel with the address electrodes 9 and vertical to the surface of the substrates 1, 2. FIG. 5(b) is a cross sectional view at a position A in FIG. 5(a) and the cutting plane is vertical to the address electrodes 9 and vertical to the surface of the substrates 1, 2. FIG. 5(c) is a cross sectional view at a position B in FIG. 5(a) and the cutting plane is vertical to the address electrodes 9 and vertical to the surface of the substrates 1, 2. In FIG. 5(a)-(c), only the cross section is shown for making the drawing easy to view while the constitution which may be seen at the bottom of the drawing paper is not illustrated. Further, FIG. 6 shows a cross sectional view along a plane shown by C in FIG. 5(a).
As shown in FIG. 5(b) and FIG. 5(c), a display cell (also referred to as a discharging cell) is formed between both of substrates 1 and 2 on every set of the transparent electrodes 5a and 5b, and a discharging space 3f is formed by both of the substrates 1, 2 and the barrier ribs 3a. A fluorescent film 14 is formed at the inside of the display cell. Further, discharge gas is sealed in the space 3f in the cell. In the display panel, as shown in FIG. 6, the barrier ribs 3a are in the form of parallel rods, and the discharging space 3f of the cell is continuous laterally (or longitudinally) and is not partitioned by the barrier ribs 3a.
When an AC voltage is applied between the electrodes 5, of the front substrate 1 and the address electrodes 9 formed to the back substrate 2, auxiliary discharging is generated in each of the cells 3f formed by the front substrate 1, the back substrate 2 and the barrier rib 3a. When AC voltage is applied between the parallel electrodes 5a, 6a and the electrodes 5b, 6b formed to the front substrate 1 on each of the cells by utilizing the auxiliary discharging, main discharge is generated. Ultraviolet rays caused by the main discharging causes the fluorescent body 14 coated in the cell to emit light. The display by the display panel is conducted by light from the fluorescent body 14 observed through the front substrate 1.
An example of the gas discharging type display device shown in FIGS. 4-6 is described in Flat Panel Display (1994 (edited by Nikkei Microdevice, 1993), page 198-201).
As a method of manufacturing such a gas discharging type color display panel, the method explained below is known.
At first, a pair of transparent substrates are provided. As the substrate used for the gas discharging color display panel, a soda glass (soda lime glass) plate having a strain point at about 450.degree. C. is generally used.
After printing an electrode paste to a predetermined pattern by a thick film printing method to one of the glass substrates (back substrate) and drying the paste at 100.degree.-150.degree. C., it is baked at 500.degree.-600.degree. C. Then, for forming a display cell as a picture element, a barrier rib-forming paste is printed in a predetermined pattern by a thick film printing method on the surface of the back electrode formed with the electrode pattern and dried at 100.degree.-150.degree. C. This forms a number of cells arranged in a matrix on the back substrate. A thick film thickness (for example, 160 to 200 .mu.m) is required for the barrier rib in order to ensure a sufficient discharging space and such a thickness can not be obtained by use of the thick film printing method only once. Accordingly, printing and drying of the barrier rib-forming paste are carried out a plurality of times. To the interior of the cells formed by the barrier ribs, red, blue and green pastes for the fluorescent body are printed in a predetermined pattern by a thick film printing method and dried at 100.degree. to 150.degree. C. followed by sintering at 500.degree.-600.degree. C. Thus, a back electrode formed with a display cell can be obtained.
A vapor deposition film of a transparent conductor, for example, ITO (indium tin oxide) is formed on the other of the glass substrates (front substrate glass plate), which is patterned to form a number of electrode patterns in parallel with each other such that two electrodes parallel with the row of the cells are disposed on every cells. Then, a buss electrode is formed to each of the electrode portions of the pattern for reducing the resistivity of the electrode. After printing a dielectric paste in a predetermined pattern on the surface formed with the electrodes by a thick film printing method and drying the same at 100.degree.-150.degree. C., it is sintered at 500.degree.-600.degree. C. Further, an MgO film is formed to the surface of the resultant dielectric film by an EB (electron beam) vapor deposition method. Thus, a front substrate formed with transparent electrodes can be obtained.
Then, the front substrate and the back substrate are aligned with the surface of the front substrate formed with the MgO film and the surface of the back substrate formed with the cell being opposed to each other, and edge portions of both of the substrates are covered with lead glass for sealing, and heated at about 450.degree. C. to effect sealing between both of the substrates. Then, air in the gap surrounded with both of the substrates and the sealed portion is evacuated from an evacuation pipe and a discharge gas is entered into the gap by way of the evacuation pipe. Finally, the evacuation pipe is chipped off to seal the discharge gas. With the procedures described above, the gas discharging type color display panel is prepared.
In the foregoing explanation, although the barrier ribs are formed to the back substrate, the barrier ribs may be formed on the front substrate or formed on both of the front substrate and the back substrate depending on the design of the display panel. Further, the electrode or the MgO film may sometimes be formed by a thick film printing method.
The method of manufacturing the display panel described above has a merit capable of manufacturing a display panel relatively easily since the barrier ribs, electrodes, the fluorescent body, etc. are formed by the thick film printing method.
As described above, in the gas discharging type display panel of the prior art, since auxiliary discharging and main discharging are conducted in an identical discharging space, light emission is caused by the auxiliary discharging also in an area where the main discharging is not conducted, so as to bring about a problem that the display panel is not capable of obtaining a sufficient contrast. If sufficient contrast is not obtained, high speed time divisional control has to be applied by a complicated driving method in order to obtain sufficient gradation for full color display. Thus, it is desirable to obtain a sufficient contrast by the structure of the gas discharging display panel.
Further, the thickness of the barrier rib has to be made as large as from 160 to 200 .mu.m in order to ensure a sufficient discharging space, but such thickness can not be obtained by only one time of the thick film printing so that the manufacturing method adopted so far provides the required thickness by repeating printing and drying of the paste for several times. However, with such a procedure, the manufacturing step is made lengthy and since alignment is conducted on every printing, the yield is worsened.
In view of the above, it is considered to dispose a partition wall substrate as an integral part of a partition wall having penetration apertures as a discharging conduction path and barrier ribs and put the partition wall substrate between the front substrate and the back substrate. If the space in the display cell is separated by the partition wall into an auxiliary discharging space and a main discharging space, since light caused by the auxiliary discharging can be shielded, the contrast is increased. Further, if the partition wall substrate having the partition wall and the barrier ribs is manufactured by integral shaping, for example, by a sand blasting method of a glass or ceramic plate as an insulator, since this can be handled as one part, no accurate alignment is required as in the case of forming the barrier ribs with the thick film printing.
However, in the methods described above, since the substrate such as of ceramics requiring difficult fabrication has to be fabricated into a complex shape, the number of steps is increased to increase the cost.